The invention relates to a method and apparatus for feeding items into a sorting system, which system includes subsystems for singulation of items such as parcels.
In mail handling operations, large quantities of items such as boxes, parcels, packages, or parts varying widely in size, must be inducted into sorter systems. A feeder system for use in processing centers takes a disordered stream of items fed to it on a conveyor and inducts them onto the sorter system. For this purpose, the feeder system ideally should perform several functions. It should, to the maximum extent possible, singulate disordered items to present them to the sorter one at a time with sufficient spacing or separation between items. It must also read destination information from the item so that the control system for the sort can track it through the system and sort it correctly. In the U.S., scannable bar codes are used for this purpose. A third important function is that items that are non-machinable because they are too large, too heavy or the like should be intercepted and removed from the system for special handling.
Singulation is an essential first step in the handling and sorting of items such as parcels or soft packages. Singulation is a process whereby a randomly input stream of items moving on a conveyor system is separated into a stream of single items spaced from each other so that a downstream process can readily perform operations on each item one at a time. Material singulation is a particular challenge in that a mixed material stream may include packages that vary greatly in size and may be piled at random one upon another, forming agglomerates of packages that are difficult to detect and separate.
According to one previously proposed method for singulation, an inclined ramp with holes for applying suction is provided. Items are allowed to slide down the ramp and then suction is applied to hold them in place on the slide. The suction is then selectively released in order release one item at a time. See Interim Report For Phase I, U.S. Postal Service Contract 104230-85-H-0002, Apr. 5, 1985, ElectroCom Automation, Inc., pages 3-10 to 3-13. This method provides one form of hold-and-release singulation, but is of doubtful utility for larger items that may be difficult to hold effectively using suction and that may tend to tumble down a slide, possibly evading the effect of suction and leaving the singulator prematurely. A hold-and-release singulator according to the present invention addresses these difficulties.
A hold-and-release singulator according to the invention includes a conveyor having a transport mechanism for carrying a group of items such as parcels, packages, containers or the like from an entry end towards an exit end of the singulator, a hold and release system that can hold items that have entered the singulator on the conveyor so that such items are not transported by the conveyor while causing one item to be transported by the conveyor, and a control system that controls operation of the conveyor and the hold-and-release system in a manner effective to remove the group of items from the exit end of the conveyor one at a time according to a removal scheme, preferably with a predetermined minimum spacing. The hold and release system can take several forms, such as a mechanism for selectively actuating a portion of the conveyor at a time to remove an item from the exit end of the conveyor, or a mechanism that can hold items off of the conveyor surface so that such items are not transported when the conveyor is running, and selectively set items onto the conveyor surface so that such items are transported when the conveyor is running. In the latter case, the control system controls operation of the conveyor and the hold-and-release system in a manner effective to hold a group of items off of the conveyor surface and then lower the items according to the removal scheme so that the items leave the exit end of the conveyor one at a time with a predetermined minimum spacing. The items may be supported from beneath by a series or array of supports which lift the items, or an arm may suspend the items from above to hold the items off of the conveyor surface.
An optional vision system for use with the singulator includes a camera that records an image of the items to be singulated by the hold-and-release system, whereby the control system operates the hold-and-release system based on item positions determined from the image. The control system may, for example, include logic for determining which supports support each item to be singulated, and logic for determining the order in which the supports should be lowered in order to singulate the items. This will generally be done by determining groups of supports that support a common item as described hereafter.
According to preferred aspect of the invention, the hold and release singulator includes a conveyor having a transport mechanism for carrying a group of items from an entry end towards an exit end of the singulator. The hold and release system of this embodiment includes an array of supports which lift items from below to hold the items off of the conveyor surface so that such items are not transported by the conveyor, and a retraction mechanism that can be operated to lower the supports beneath one item to permit the item to be transported by the conveyor. A vision system includes a camera that records an image of the items to be singulated by the hold-and-release system. The control system controls operation of the conveyor and the hold-and-release system in a manner effective to remove the group of items from the exit end of the conveyor one at a time according to a removal scheme, which scheme includes logic for determining which supports support each item to be singulated using the image, and logic for determining the order in which the supports should be lowered in order to singulate the items. The conveyor transport mechanism preferably has a series of parallel belts positioned to carrying items from the entry end of the singulator towards the exit end of the singulator, so that the supports can be arranged in rows between the belts. An infeed conveyor may be provided adjacent the entry end of the singulator, and suitable means (such as the image data or a photocell) used to determine when a sufficient group of items has passed onto the singulator conveyor from the infeed conveyor. The control system then further includes logic for stopping the infeed conveyor when the hold-and-release system is in operation.
A method of singulating a group of items according to the invention includes the steps of:
(a) transporting a group of items onto a conveyor of a hold and release singulator, which conveyor includes a transport mechanism which carries the group of items from an entry end towards an exit end of the singulator;
(b) operating a hold-and-release system to hold items that have entered the singulator on the conveyor so that such items are not transported by the conveyor, while causing one item to be transported by the conveyor;
(c) controlling operation of the conveyor and the hold-and-release system in a manner effective to remove the group of items from the exit end of the conveyor one at a time according to a removal scheme; and
(d) repeating steps (a)-(c) with successive groups of items. This is largely a batchwise operation, but where a vision system is used, the singulator conveyor can run continuously all or part of the time when the control logic determines from the image data that the items moving on the conveyor are sparse and already widely spaced. Step (b) may comprise holding items off of the conveyor surface so that such items are not transported when the conveyor is running, or selectively actuating a portion of the conveyor at a time to remove an item from the exit end of the conveyor. In a preferred embodiment, the items are transported on an infeed conveyor to the entry end of the singulator, and the infeed conveyor stops when the hold-and-release system is in operation. If an array of supports are provided as part of the hold and release system, steps (b) and (c) preferably further comprise determining which supports underlie items, determining groups of supports among those underlying items which underlie the same item, raising groups of supports which extend through the singulator conveyor in order to lift the items off of the singulator conveyor surface, and successively lowering groups of supports which support each item.
An alternate method of singulating a group of items according to the invention can be employed when the items enter the singulator in a known formation, such as side-by-side forming a square or rectangle. Such a method includes the steps of:
(a) transporting a group of items onto a conveyor of a hold and release singulator in a predetermined formation, which conveyor includes a transport mechanism which carries the group of items from an entry end towards an exit end of the singulator;
(b) operating a hold-and-release system to hold items that have entered the singulator on the conveyor so that such items are not transported by the conveyor, while causing one item to be transported by the conveyor;
(c) controlling operation of the conveyor and the hold-and-release system in a manner effective to remove the group of items from the exit end of the conveyor one at a time according to a removal scheme based on the predetermined formation; and
(d) repeating steps (a)-(c) with successive groups of items. Such a method may be used, for example, with successive layers removed from a stack as described further below.
Singulation using the system and method of the invention can be precise or approximate depending on the removal scheme selected, as described hereafter. The occurrence of multiples, i.e., parcels resting upon each other or abutting one another will occasionally cause two or more items to leave the hold-and-release singulator unseparated. These and other aspects of the invention are set forth in the following detailed description.